The First Trimester Of Pregnancy: Guide And What To Expect

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The three trimesters of pregnancy are distinguished according to the gestational age and development of the fetus. The first trimester of pregnancy begins from the first day of your last menstrual cycle and lasts until the end of week 12 (1).

The first trimester is the most crucial period for the baby’s development (2). A woman also undergoes several physical and mental changes in this time. Read this post to know all about what to expect from your body and the baby’s growth in the first trimester.

First Trimester Changes In The Mother’s Body

The experts at UNICEF enlist the following as the common symptoms of pregnancy in the first trimester (3).

1. A missed period

A missed period is usually the first sign of pregnancy. However, a woman can miss her period for reasons other than pregnancy as well.

2. Implantation bleeding

Implantation bleeding usually happens six to 12 days after ovulation when a fertilized egg implants itself in the lining of the uterus wall (4). It is usually not a cause of concern but must be brought to the doctor’s attention.

3. Breast tenderness

Hormones of pregnancy, such as estrogen, progesterone, and prolactin, increase the sensitivity and tenderness of the breasts (5).

4. Constipation

Increasing progesterone during pregnancy causes the intestinal muscles to relax, causing food and waste to move slower through the digestive system leading to constipation (6).

5. Vaginal discharge

During pregnancy, the cervix and the walls of the vagina become softer, and increased levels of progesterone cause an increase in the production of fluid. Increased vaginal discharge is normal, but if you notice any unusual color or foul smell, it is essential to notify your doctor about it (7).

6. Fatigue

Hormonal changes, especially the steep increase in progesterone, are responsible for fatigue in the first trimester (8).

7. Food likes and dislikes

It is common to develop a craving for some foods and dislikes or aversion to others in the first trimester (3).

8. Frequent urination

Increased pressure on the urinary bladder by the expanding uterus and the baby’s weight can lead to frequent urination (9).

9. Mood swings

Mood swings during pregnancy happen due to a combination of factors such as physical stress, fatigue, metabolic changes, and an increase in estrogen and progesterone. Substantial hormonal fluctuations of the first trimester can affect the levels of neurotransmitters, too. Neurotransmitters are chemicals released by the brain and play a role in mood regulation(10).

10. Morning sickness

Morning sickness is characterized by nausea and vomiting in the first trimester. It is quite common, and at least seven in ten women experience morning sickness in the first trimester (11).

11. Weight gain

0.5 to 2.0 kilograms or 1.1 to 4.4 pounds of weight gain is normal in the first trimester. If you lose or gain more than five to ten percent of your pre-pregnancy weight in the first trimester, you must speak to your healthcare provider (12).

12. Headache

Hormonal changes and an increase in blood volume lead to headaches in the first trimester of pregnancy (13).

13. Heartburn

Hormonal changes often lead to heartburn in the first trimester of pregnancy (14).

14. Leg cramps

Leg cramps are most common in the third trimester but may occur at any time in pregnancy. Weight gain and changes in blood circulation in pregnancy can lead to leg cramps (15).

15. Lower back and pelvic pain

Ligaments in the body become softer in pregnancy to aid childbirth. Soft ligaments can put a strain on the joints of the pelvis and lower back, leading to lower back and pelvic pain (16).

Dos And Don’ts In The First Trimester

Follow your gynecologist’s advice for self-care during pregnancy. The following are common dos and don’ts during the first trimester (17).


  • Continue your prenatal vitamins containing at least 400mcg of folic acid
  • Continue mild exercises
  • Incorporate lean meats, fruits, vegetables, and fiber into your diet
  • Stay hydrated
  • Focus on eating a balanced diet instead of counting calories


  • Avoid alcohol
  • Limit caffeine intake
  • Avoid contact with cat litter as it carries a risk of developing toxoplasmosis
  • Avoid consuming uncovered, undercooked, and raw meat
  • Avoid high-mercury fishes
  • Avoid direct or second-hand cigarette smoke
  • Do not consume unpasteurized dairy products

Symptoms That Need Medical Attention

You may talk to your healthcare provider if you notice any of these symptoms in your first trimester (3)(18).

  • Severe cramping
  • Severe or long-lasting headache
  • Dizziness
  • Chills
  • Breathlessness, weakness, or racing heart
  • Continuous or severe pain on one side of the abdomen
  • Pain on the tip of the shoulder
  • Strong pain in your lower abdomen
  • Fever over 38°C or 100°F
  • Smelly vaginal discharge
  • Painful urination
  • Bright red vaginal bleeding
  • Severe vomiting
  • A blow to the stomach from an accident, violence, fall, or crash

Baby’s Growth In The First Trimester

By the end of the first trimester, the baby turns from being a little ovum to a six-centimeter long fetus. The baby’s heart begins to beat, and the brain and the spinal cord begin to form. The hands and legs appear as tiny buds. The circulatory system, nervous system, digestive system, and urinary system begin to develop. Tooth buds begin to form.

By the end of 12 weeks, the external genitalia, fingers, toenails, eyelids, and larynx begin to form. The fetal movement also begins, although the mother cannot feel the fetal movement yet. Read more about fetal development in the first trimester here.

The fetus is most vulnerable in the first trimester. In this time period, all major organs and body systems are forming. However, the systems are not fully formed to support the fetus’ survival outside the mother’s body yet (19). If the fetus is exposed to conditions and substances, such as drugs, German measles, radiation, tobacco, and toxic substances, the newly formed organs may sustain damage. Therefore, it is vital to avoid substances and habits that could be hazardous to the fetus.

Things To Consider During The First Trimester

Apart from physical changes, pregnancy and childbirth will affect many aspects of your life. You may take some time pondering and deciding over the following factors in the first trimester.

1. Informing your friends, family, and employer

The risk of miscarriage is highest in the first trimester. Many women may prefer waiting for 12 weeks before declaring their pregnancy. However, it is each woman’s choice to decide when to tell others about their pregnancy.

You should consider whether you will continue to work after delivering your child or not and if your employer offers maternity leave or not. Based on these factors, you may decide on when to inform your employer about your pregnancy.

2. Deciding your birth plan

You must research the available options and decide on your birth plan. You must decide on your preferred place of childbirth and the preferred form of delivery. You may also think about your birth companions, your specific preferences regarding the birth environment, your choices for labor pain relief, and your choice of procedures to be avoided.

3. Paying for care

Many women worry about the costs of medical bills during their pregnancy. However, in several nations, many good insurance plans that cover prenatal and natal care. Talk to the hospital authorities to know the available insurance options.

You might know of your pregnancy only after a few weeks into the first trimester of pregnancy. Once you know of your pregnancy, it is recommended that you seek advice from your OB/GYN regarding your prenatal care. Adequate nutrition, hydration, and sleep can help you navigate through the hiccups of the first trimester of pregnancy.


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  1. Everything you need to know about the first trimester (weeks 1 to 12).
  2. Pregnancy the three trimesters.
  3. Your first trimester guide.
  4. What is Implantation Bleeding?
  5. Breast changes during pregnancy.
  6. Constipation in Pregnancy.
  7. Vaginal discharge during pregnancy.
  8. First Trimester Fatigue.
  9. What Causes Frequent Urination During Pregnancy?
  10. Mood Swings During Pregnancy.
  11. Morning Sickness.
  12. Weight Gain During Pregnancy
    By Trimester.
  13. Headaches in Early Pregnancy.
  14. Indigestion and heartburn in pregnancy.
  15. Leg Cramps During Pregnancy.
  16. Back pain in pregnancy.
  17. First Trimester: Symptoms and Screening.
  18. Warning signs during pregnancy.
  19. The First Trimester.